Chemistry Honors – Unit 6 Name: _________________________________ Missing Element Prediction Period: _______ Date: ___________________ So far we have learned that the periodic table of elements is arranged according to the Periodic Law, which states that when elements are arranged according to increasing atomic number, there is a recurrence of similar physical and chemical properties at regular intervals This Law shows that the physical and chemical properties of elements are directly related to their electronic structures. As a result of the periodic nature of the Periodic Table, properties of an element can, in some cases, be estimated by averaging properties of the preceding and following elements in the same group. This was how Mendeleev predicted the properties of elements unknown in his time. He was so certain of his conclusions, that he left gaps in this table for the missing elements with the predicted properties. Mendeleev’s fame rests largely on the correctness of these predictions. When the elements were discovered, they fit in exactly as he had expected. As an example, suppose that krypton is unknown and you want to answer the following question: Estimate the boiling point of krypton, given that the boiling point of argon is –186 C and that of xenon is –112 C. In the periodic table, krypton is preceded by argon and followed by xenon. Taking the average of these boiling points gives us…(show your work.) The estimated boiling point of krypton, –149 C, is within 5% of the known boiling point of –157 C. As another example, consider the prediction of the formulas of chemical compounds based on periodic table relationships. What formula would you predict for the compound formed between carbon and sulfur? Keep in mind that carbon and oxygen form carbon dioxide (CO2). Consulting the periodic table shows that sulfur and oxygen are in the same family. As a result, sulfur and oxygen behave the same chemically, and so the prediction would be carbon disulfide (CS2). Answer the following questions, based on the discussion above. Show calculations! 1. One of the elements undiscovered in Mendeleev’s time was germanium. Given that the melting points of silicon and tin are 1410 C and 232 C respectively, estimate the melting point of germanium. 2. Estimate the melting point of rubidium. The melting points of potassium and cesium are 64 C and 29 C respectively. Would you expect the melting point of sodium to be higher or lower than that of rubidium? 3. These are formulas for known compounds: NaI, MgCl2, CaO, Al2O3, and CCl4. Predict the formula of a compound formed from each pair of elements: (a) Si and F (b) Al and S (c) K and Cl (d) Ca and Br (e) Ba and O 4. Which family of elements is so lacking in chemical reactivity that its elements were originally regarded as “inert?” Give the name and the group number. 5. The two most recently named elements are Flerovium (Z = 114) and Livermorium (Z = 116). How many valence electrons would you expect each to have? 6. Ununseptum (Z = 117)has been created for nanoseconds. If it were to be more stable, what state would you expect it to exist in at room temperature? Explain. Discuss how you could predict its boiling point (what information would you need?)